Antenna systems for direction finding (DF) or direction-of-arrival (DOA) of wireless signals such as RF (radio frequency) or microwave signals usually require finding an azimuth and an elevation of the arriving signals.
Antenna systems usually estimate each property (azimuth angle or elevation angle) separately requiring a complicated and usually expensive constructions and designs to achieve high level and accurate estimations of azimuth and elevation.
Most systems use two different sub systems to estimate each property of the arriving signal separately. One commonly known method is to use two multimodal antennas wherein one antenna is used to estimate the azimuth of the arriving signal and the two multimodal antennas are used to estimate the elevation, using interferometry techniques. In these methods, each of multimodal antennas produces at least two modes: a zero mode and a first-order phase mode allowing extracting the azimuth using one of the antennas and the elevation using the other antenna. The azimuth and elevation are extracted separately using two separate techniques: a multimodal technique is used for extracting the azimuth and an interferometry technique is used for extracting the elevation.
U.S. Pat. No. 7,427,953, which is incorporated herein by reference in its entirety, discloses an antenna system for determining the DOA of received signals, where the system includes two antenna arrays, each having a plurality of antenna elements, two first stage multi-mode-port matrices, at least one second stage multi-mode-port matrix, an azimuth phase detector, an elevation amplitude detector, a plurality of phase shifters and a transceiver. The antenna arrays and the first stage multi-mode-port matrices form a plurality of orthogonal omnidirectional modes. Each of the phase modes has a characteristic phase set. Two of the modes' phases are used to determine DOA in azimuth. The second stage multi-mode-port matrix forms a sum-mode and a difference-mode used to determine the elevation of the received signals. The sum and difference method is an alternative method to find the elevation by comparing amplitudes instead of comparing phases as required in interferometry. The second antenna may also include a multimodal omnidirectional antenna so the two equal antennas are utilized to shape a radiation pattern of low side-lobes of the transmitted signal in the direction characterized by the measured elevation and azimuth.
U.S. Pat. No. 3,568,203, which is incorporated herein by reference in its entirety, discloses a DF antenna assembly comprising a horn antenna structure and associated microwave circuitry capable of determining the azimuth of a received signal. The assembly enables producing signals at output ports of a hybrid circuit that change in phase as a linear function of the azimuth angle of the arriving signal, where a comparison of these signals with a reference mode enables determining the azimuth angle of arrival of the signal received at the antenna. The elevation is found separately by a second antenna that is perpendicular to the horizon plane, wherein the second antenna comprises a linear array of at least two omnidirectional antenna elements (dipoles), and the elevation is found by the interferometry technique by measuring the phase difference between two dipoles of the second antenna.
U.S. Pat. No. 2,954,558, which is incorporated herein by reference in its entirety, discloses an antenna system comprising a single biconical radiator and microwave energy propagating means that allow extracting the azimuth of arriving signals regardless of their elevation by enabling to produce only TEM and TE10 radial-line modes responsive of the energy from the arriving signals, wherein the radial-line modes are transformed to TEM and TE11 coaxial-line modes. The TEM and TE11 modes are propagated through four rectangular waveguides and waveguide transition means, where the TEM mode establishes equal signals in phase and amplitude through the waveguides and the TE11 mode establishes respective oppositely phased signals, where the azimuth of the arriving signals is extracted from the phase difference between the TEM and TE11 modes.
All of the above mentioned patents and patent applications disclose systems and assemblies that only allow extracting of the azimuth independently of the elevation of an arriving signal, whereas another process and measuring and more hardware is required to measure the elevation of the arriving signal. The additional process may require a different arrangement of the system only enabling a separate process for determining the elevation of the arriving signal.